CN103179058A - Method and apparatus for estimating channel impulse response length - Google Patents

Abstract

The embodiment of the invention discloses a method and an apparatus for estimating a channel impulse response length. The embodiment comprises the steps of treating frequency domain data subjected to synchronization and frequency offset compensation through least square (LS) criterion channel estimation in a pilot frequency, so as to obtain channel frequency domain response in the pilot frequency; interpolating the channel frequency domain response in the pilot frequency to obtain channel frequency domain response at the data; and estimating a channel impulse response length of the channel frequency domain response according to time domain channel responses corresponding to the channel frequency domain response in the pilot frequency and the channel frequency domain response at the data. The embodiment disclosed by the invention aims at solving the problem that the existing channel estimation method is not applicable to an aviation broadband wireless communication system which is complex and changeable in channel environment, and the embodiment can improve channel estimation performance.

Description

The method of estimation of channel impulse response length and device

Technical field

The embodiment of the present invention relates to aviation system of broadband wireless communication field, relates in particular to a kind of method of estimation and device of channel impulse response length.

Background technology

Developing rapidly of civil aviaton's communication service, the particularly rapid growth of earth-space communication business promote the civil aviation communication network to develop from the arrowband to the broadband.OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology becomes the key technology of aviation system of broadband wireless communication with characteristics such as its high transfer rate, high spectrum utilization, strong anti-multipath interference performances.The OFDM technology is responsive especially to frequency deviation, and the precision of channel estimating will directly affect the performance of OFDM technology, and therefore, channel estimation methods is the key that realizes that the OFDM technology is used in the aviation system of broadband wireless communication.

Usually, channel estimation methods comprises least square (Least Square, LS) channel estimation methods and improved LS channel estimation methods, wherein, the LS channel estimation methods does not consider to receive the noise in signal, so be subjected to the impact of white Gaussian noise very large, especially when signal to noise ratio was lower, channel estimating performance was relatively poor; For improved LS channel estimation methods, when the translational speed increase of aircraft, when Doppler frequency shift increased, channel estimating performance descended rapidly; And, in the aviation system of broadband wireless communication, channel circumstance is complicated and changeable, comprise take off, landing, runway slides and the scene such as stop, channel impulse response length under different scenes is constantly to change, and the channel impulse response length in improved LS channel estimation methods is fixed, and therefore, channel estimating performance is relatively poor.

Summary of the invention

The embodiment of the present invention provides a kind of method of estimation and device of channel impulse response length, be applied in the channel estimating scene of civil aviaton's vacant lot system of broadband wireless communication, be not suitable for problem in channel circumstance aviation system of broadband wireless communication complicated and changeable in order to solve existing channel estimation methods, can improve channel estimating performance.

First aspect the invention provides a kind of method of estimation of channel impulse response length, is applied to comprise in the channel estimating scene of civil aviaton's vacant lot system of broadband wireless communication:

With the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place, obtain the channel frequency domain response at pilot tone place;

The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation;

According to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

Second aspect the invention provides a kind of channel impulse response length estimation unit, is applied to the aviation system of broadband wireless communication, comprising:

The first processing module is used for the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place obtained the channel frequency domain response at pilot tone place;

The second processing module is used for the channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation;

The 3rd processing module is used for time domain channel response corresponding to channel frequency domain response according to the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

The embodiment of the present invention obtains the channel frequency domain response at pilot tone place by with the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place; The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation; According to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.Thereby can realize: in the aviation mobile communications system under the changeable scene of channel circumstance, the present embodiment can be according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at pilot tone place and data places, estimation obtains channel impulse response length, this channel impulse response length changes in real time with the channel environmental evolution, therefore, go in channel circumstance aviation system of broadband wireless communication complicated and changeable, and can improve channel estimating performance.

Description of drawings

The schematic flow sheet of the method for estimation of the channel impulse response length that Fig. 1 provides for one embodiment of the invention;

Fig. 2 is the schematic flow sheet of the channel estimation methods of civil aviaton's vacant lot system of broadband wireless communication of using of the embodiment of the present invention;

The structural representation of the estimation unit of the channel impulse response length that Fig. 3 provides for another embodiment of the present invention.

Embodiment

In order to guarantee that aviation wideband OFDM mobile communication system can have a good inhibitory action to noise under different channel circumstances, need dynamically to follow the tracks of the variation of channel impulse response length.The invention provides a kind of method of estimation of channel impulse response length, can be adaptively the size of channel impulse response estimation length in real time, thereby guarantee channel estimating performance under aviation broad-band channel condition complicated and changeable.

The schematic flow sheet of the method for estimation of the channel impulse response length that Fig. 1 provides for one embodiment of the invention, as shown in Figure 1:

101, with the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place, obtain the channel frequency domain response at pilot tone place.

After receiver receives data, need to first carry out synchronously, generally need to further carry out frequency deviation to signal after synchronous success and estimate and compensate.For example, when the base station during to user terminal to transmit data, receive and be the receiver of subscriber terminal side, during to base station transmission data, receiver is the receiver of base station side when user terminal.

The frequency-domain data matrix at the pilot tone place after assumes synchronization and compensate of frequency deviation is the Y(diagonal matrix), the pilot tone place frequency-domain data matrix of the transmitting terminal of local storage is the X(diagonal matrix), H _LSPilot tone place channel frequency domain response truth value matrix under the LS criterion uses least square criterion, obtains:

minf(H _LS)=min{(Y-XH _LS) ^H(Y-XH _LS)}

Can be got by the calculus theorem, make function minf (H _LS) get minimum value, need to make this function to H _LSPartial derivative be 0, namely Obtain the estimated value matrix of the channel frequency domain response at the pilot tone place under the LS criterion:

102, the channel frequency domain response with described pilot tone place obtains the channel frequency domain response at data place through interpolation.

Need to prove, interpolation algorithm can be prior art, usually, the algorithm that interpolation adopts can be selected different interpolation algorithms according to system requirements and system pilot tone pattern used, suppose that the present embodiment adopts the first-order linear interpolation algorithm, wherein, the first-order linear interpolation algorithm is to utilize two adjacent frequency pilot signs to carry out linear interpolation.

Suppose first to carry out the interpolation of two-dimension pilot frequency pattern time-axis direction, interpolation formula is:

$H(k,i)=(1-\frac{p}{{\mathrm{\Δ}}_t})H(k,q{\mathrm{\Δ}}_t)+\frac{p}{{\mathrm{\Δ}}_t}H(k,(q+1){\mathrm{\Δ}}_t);$

Wherein, k represents k subcarrier, and i represents i orthogonal frequency division multiplexi OFDM symbol, and p, q are intermediate variable, there is no concrete physical significance, just facilitate the expression of formula, 1≤p≤Δ _t-1, q Δ _tThe Δ of＜i＜(q+1) _t, q=0,1,2....; Δ _tSpacing for adjacent two pilot tones on time shaft.

If need to carry out linear interpolation in the frequency axis direction, interpolation formula is:

$H(k,i)=(1-\frac{p}{{\mathrm{\Δ}}_f})H(q{\mathrm{\Δ}}_f,i)+\frac{p}{{\mathrm{\Δ}}_f}H((q+1){\mathrm{\Δ}}_f,i)$

Wherein, k represents k subcarrier, and i represents i orthogonal frequency division multiplexi OFDM symbol, and p, q are intermediate variable, there is no concrete physical significance, just facilitate the expression of formula, the q Δ _fThe Δ of＜k＜(q+1) _f, 1≤p≤Δ _f-1, Δ _fIt is the spacing of adjacent two pilot tones on frequency axis.

103, according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

Suppose in the ideal case, the channel impulse response coefficient is positioned in channel impulse response length, white Gaussian noise is uniformly distributed in all channel sample, and the channel time domain impulse response true value of i orthogonal frequency division multiplexi OFDM symbol on k subcarrier is:

$h_{k,i}=\left\{\begin{array}{c}{h}_{k,i}^L,0\&le;k<L\\ 0,L\&le;k<N\end{array}\right.-----\left(A\right)$

Step 103 is specifically as follows:

1031, obtained the accumulation mean square error function of channel impulse response by the definition of accumulation mean square error.

Wherein, accumulation mean square error function is:

Wherein,

Be the estimated value of the channel time domain impulse response of i orthogonal frequency division multiplexi OFDM symbol on k subcarrier, comprise noise component(s).

Can further obtain accumulating the mean square error function by formula (A) is: $e\left(L\right)=E\left[\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{|{\hat{h}}_{k,i}-h_{k,i}|}^2\right]=\underset{k=L}{\overset{N-1}{\mathrm{\&Sigma;}}}E\left[{\left|{\hat{h}}_{k,i}\right|}^2\right]+L\&CenterDot;{\mathrm{\&sigma;}}_{\mathrm{noise}}^2,$ This function is concave function, and minimum value is arranged, and will accumulate the channel impulse response length that L value corresponding to mean square error function e (L) minimum value is defined as i orthogonal frequency division multiplexi OFDM symbol;

Wherein,

Be the noise error of estimation, h _k,iThe channel time domain response true value at described data place, Be the channel time domain response estimation value at described data place, L represents channel impulse response length, and N represents total number of subcarrier, 0≤k≤N, M represents the number of orthogonal frequency division multiplexi OFDM symbol, and i represents i orthogonal frequency division multiplexi OFDM symbol, 1≤i≤M;

Hence one can see that, in the aviation mobile communications system under the changeable scene of channel circumstance, even the channel frequency domain response at the channel frequency domain response at pilot tone place and data places changes along with the variation of channel circumstance, the present embodiment is according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at pilot tone place and data places, and the channel impulse response length that estimation obtains also can change in real time with the channel environmental evolution.

1032, the channel impulse response length of M OFDM symbol is got maximum, as the channel impulse response length of described channel frequency domain response.

In the present embodiment, the channel impulse response length of M OFDM symbol is got maximum, make in time domain channel response the corresponding number that contains the noise element ZF more, thereby the noise that removes is also more, channel estimating just more accurate.

Fig. 2 is the schematic flow sheet of the channel estimation methods of civil aviaton's vacant lot system of broadband wireless communication of using of the embodiment of the present invention, as shown in Figure 2:

With the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place, obtain the channel frequency domain response at pilot tone place.The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation.

Suppose in the ideal case, the channel impulse response coefficient is positioned in channel impulse response length, white Gaussian noise is uniformly distributed in all channel sample, and i the channel frequency domain impulse response of orthogonal frequency division multiplexi OFDM symbol on k subcarrier is:

$H\left(k\right)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}h\left(n\right)\&CenterDot;e^{-j\frac{2\mathrm{\&pi;nk}}{N}},$ J represents the imaginary part of plural number on mathematics;

This formula is rewritten into $H(k,i)=\frac{1}{\sqrt{N}}\underset{n=0}{\overset{L-1}{\mathrm{\&Sigma;}}}h\left(n\right)\&CenterDot;e^{-j\frac{2\mathrm{\&pi;nk}}{N}};$

Wherein, N represents total number of subcarrier, 0≤k≤N; L represents channel impulse response length.

The frequency domain response vector of each OFDM symbol is

Wherein, matrix F is Fourier transform matrix, N _DBe the number of useful subcarrier, N is not less than N _D, when including with subcarrier and virtual subnet carrier wave in N, N is greater than N _D.When only including in N when using subcarrier, N _DEquate with N.

Matrix F is made QR decomposes, obtain matrix:

Wherein,

Normalization matrix,

Upper triangular matrix, wherein, N _DThe element that-L is capable is zero.

Above-mentioned steps 102 is carried out obtaining after QR decomposes through the channel frequency domain response H that interpolations obtain the data places: further be written as:

Wherein, F is Fourier transform matrix, and h is time-domain response matrix corresponding to frequency domain response H.

On mathematical theory, H=Fh is arranged, but in actual applications, have noise in channel estimating, therefore, need to be superimposed with noise

Wherein, F=QR is mathematical a kind of matrix disassembling method, is called matrixQRdecomposition.

With the transposition of channel frequency domain response H premultiplication Q, namely the right and left of formula multiply by respectively Q ^H, obtain vector $\hat{g}:Q^H{\hat{H}}_{\mathrm{LS}}=Q^H(\mathrm{QRh}+\hat{W})=\mathrm{Rh}+Q^H\hat{W};$

Because R is upper triangular matrix, N is arranged _DThe capable neutral element of-L, first of above-mentioned the right only has a front L element, rear N as can be known _D-L element is zero, and second, equation the right is noise item.

Suppose

Wherein, a front L element mainly comprises channel impulse response, rear N _D-L element mainly comprises noise.Therefore a front L element is the useful data that we need, be the further impact of noise reduction on estimated performance, we can make rear N _D-L noise element ZF obtains:

Final channel frequency response is:

The embodiment of the present invention obtains the channel frequency domain response at pilot tone place by with the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place; The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation; According to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.Thereby can realize: in the aviation mobile communications system under the changeable scene of channel circumstance, the present embodiment can be according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at pilot tone place and data places, estimation obtains channel impulse response length, this channel impulse response length changes in real time with the channel environmental evolution, therefore, go in channel circumstance aviation system of broadband wireless communication complicated and changeable, and can improve channel estimating performance.

The structural representation of the estimation unit of the channel impulse response length that Fig. 3 provides for another embodiment of the present invention is applied to as shown in Figure 3, comprising in the channel estimating scene of civil aviaton's vacant lot system of broadband wireless communication:

The first processing module 31 is used for the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place obtained the channel frequency domain response at pilot tone place;

The second processing module 32 is used for the channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation;

The 3rd processing module 33 is used for time domain channel response corresponding to channel frequency domain response according to the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

For instance, described the 3rd processing module 33 specifically is used for:

Utilize accumulation mean square error function: $e\left(L\right)=E\left[\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{|{\hat{h}}_{k,i}-h_{k,i}|}^2\right]=\underset{k=L}{\overset{N-1}{\mathrm{\&Sigma;}}}E\left[{\left|{\hat{h}}_{k,i}\right|}^2\right]+L\&CenterDot;{\mathrm{\&sigma;}}_{\mathrm{noise}}^2,$ To accumulate L value corresponding to mean square error function e (L) minimum value and be defined as the channel impulse response length of i orthogonal frequency division multiplexi OFDM symbol;

Wherein,

Be the noise error of estimation, h _k,iThe channel time domain response true value at described data place,

Be the channel time domain response estimation value at described data place, L represents channel impulse response length, and N represents total number of subcarrier, 0≤k≤N, M represents the number of orthogonal frequency division multiplexi OFDM symbol, and i represents i orthogonal frequency division multiplexi OFDM symbol numbers, 1≤i≤M;

The channel impulse response length of M OFDM symbol is got maximum, as the channel impulse response length of described channel frequency domain response.

The embodiment of the present invention obtains the channel frequency domain response at pilot tone place by with the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place; The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation; According to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.thereby can realize: in the aviation mobile communications system under the changeable scene of channel circumstance, even the channel frequency domain response at the channel frequency domain response at pilot tone place and data places changes along with the variation of channel circumstance, the present embodiment is according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at pilot tone place and data places, the channel impulse response length that estimation obtains also can change in real time with the channel environmental evolution, therefore, go in channel circumstance aviation system of broadband wireless communication complicated and changeable, and can improve under the changeable scene of channel estimating performance channel circumstance in the aviation mobile communications system, the present embodiment can be according to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at pilot tone place and data places, estimation obtains channel impulse response length, this channel impulse response length changes in real time with the channel environmental evolution, therefore, go in channel circumstance aviation system of broadband wireless communication complicated and changeable, and can improve channel estimating performance.

It should be noted that at last: above embodiment only in order to technical scheme of the present invention to be described, is not intended to limit; Although with reference to previous embodiment, the present invention is had been described in detail, those of ordinary skill in the art is to be understood that: it still can be modified to the technical scheme that aforementioned each embodiment puts down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the protection range of various embodiments of the present invention technical scheme.

Claims (4)

1. the method for estimation of a channel impulse response length, be applied to it is characterized in that in the channel estimating scene of civil aviaton's vacant lot system of broadband wireless communication, comprising:

With the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place, obtain the channel frequency domain response at pilot tone place;

The channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation;

According to the time domain channel response corresponding to channel frequency domain response at the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

2. method according to claim 1, is characterized in that, described according to described pilot tone place channel frequency domain response and the time domain channel response corresponding to channel frequency domain response at described data places, the channel impulse response length of the described channel frequency domain response of estimation comprises:

Utilize accumulation mean square error function: $e\left(L\right)=E\left[\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{|{\hat{h}}_{k,i}-h_{k,i}|}^2\right]=\underset{k=L}{\overset{N-1}{\mathrm{\&Sigma;}}}E\left[{\left|{\hat{h}}_{k,i}\right|}^2\right]+L\&CenterDot;{\mathrm{\&sigma;}}_{\mathrm{noise}}^2,$ To accumulate L value corresponding to mean square error function e (L) minimum value and be defined as the channel impulse response length of i orthogonal frequency division multiplexi OFDM symbol;

Wherein,

Be the noise error of estimation, h _k,iThe channel time domain response true value at described data place,

Be the channel time domain response estimation value at described data place, L represents channel impulse response length, and N represents total number of subcarrier, 0≤k≤N, M represents the number of orthogonal frequency division multiplexi OFDM symbol, and i represents i orthogonal frequency division multiplexi OFDM symbol numbers, 1≤i≤M;

The channel impulse response length of M OFDM symbol is got maximum, as the channel impulse response length of described channel frequency domain response.

3. the estimation unit of a channel impulse response length, be applied to it is characterized in that in the channel estimating scene of civil aviaton's vacant lot system of broadband wireless communication, comprising:

The first processing module is used for the least square criterion LS channel estimating of the frequency domain data after synchronous and compensate of frequency deviation through the pilot tone place obtained the channel frequency domain response at pilot tone place;

The second processing module is used for the channel frequency domain response at described pilot tone place is obtained the channel frequency domain response at data place through interpolation;

The 3rd processing module is used for time domain channel response corresponding to channel frequency domain response according to the channel frequency domain response at described pilot tone place and described data places, the channel impulse response length of the described channel frequency domain response of estimation.

4. device according to claim 3, is characterized in that, described the 3rd processing module specifically is used for:

Utilize accumulation mean square error function: $e\left(L\right)=E\left[\underset{k=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{|{\hat{h}}_{k,i}-h_{k,i}|}^2\right]=\underset{k=L}{\overset{N-1}{\mathrm{\&Sigma;}}}E\left[{\left|{\hat{h}}_{k,i}\right|}^2\right]+L\&CenterDot;{\mathrm{\&sigma;}}_{\mathrm{noise}}^2,$ To accumulate L value corresponding to mean square error function e (L) minimum value and be defined as the channel impulse response length of i orthogonal frequency division multiplexi OFDM symbol;

Wherein,

Be the noise error of estimation, h _k,iThe channel time domain response true value at described data place,

Be the channel time domain response estimation value at described data place, L represents channel impulse response length, and N represents total number of subcarrier, 0≤k≤N, M represents the number of orthogonal frequency division multiplexi OFDM symbol, and i represents i orthogonal frequency division multiplexi OFDM symbol numbers, 1≤i≤M;

The channel impulse response length of M OFDM symbol is got maximum, as the channel impulse response length of described channel frequency domain response.

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